Linear power supply project

[pqass]

The "ref" supply NEEDS to be bipolar (have 3 output posts), that is, have  +12V, 0V/GND, and -12V outputs.
Measuring DCV between +12V and -12V posts with a multimeter should read +24V.
That GND must be connected to +S/+OUTPUT.

My ref transformer is a DP241-5-28 2x14 .400 mA centertap. That will give me my ground for the TL431s, and the fully isolated supply. At least that is what I think will happen.

Using the center tap as GND, am I correct?

Yes. 
See attached (first power supply) and simulation here.
Falstad doesn't have 7812/7912 regulators so I just labelled the place where they belong; follow your full schematic.  Notice the GND symbol on the transformer CT, between bulk caps, 7812/7912 middle pins,  anode of lower TL431, and center output connection.

The +5VREF is derived from the +12 as you've done with resistor+2*TL431 to GND (not the -12V post).

This is good to know because I used -12v for it. I am still not sure how they work to create 5v. But they sure do.

TL431 work like zeners; they shunt/clamp the voltage to their Vz voltage (or programmed via divider resistors on the adjust pin).   The 1K resistor is important otherwise you'll kill the zener/TL431.  However, shunt regulators are only good for low current loads or for reference use (your case).  See here and here. 

The "bulk" supply can be just +12 (to +20V) between 2 output posts (not bipolar).

One of the supplies must be fully isolated from PE; have NO continuity from any output post to PE or the (wide) neutral prong (on a polarized wall plug).  The latter shouldn't really exist but check anyway.

I have the Transformer a 266L24 2x12 and it can be a 2a or 4a depending on using one or two windings selected by the range switch. I understand I can wire it and use it like a center tap. GND the chassis with the PE not the center winding like the REf. Is that correct?

I think I am just going to wire the Transformers and the bridges and at least know my power is correct.

See attached (second "bulk" power supply).   
You still want to keep both ref and bulk supplies isolated from PE; leave that option for the user on the front panel.
Fortunately, the 266L24 secondaries can be wired in series or parallel.  See attached for how to wire a DPDT switch for series/parallel duty (from this "Series/Parallel Switching" diagram).  The 470R resistor (R1) is to discharge the cap when changing the switch position to the lower voltage.   However, you'll likely need another pole (3PDT) for the switch to short R32+R33 in the CREF generation part of the complete schematic (not shown here). 

Wire the primaries for the DP241-5-28 transformer the same way as shown in the Hammond connection diagram (notice the dots on the windings).  In the DP251-5-28 case, F2 connected to F1 is one mains phase and S2 connected to S1 is the other mains phase.      Don't make a mistake or you'll kill the transformer; wire up the mains fuse.

Before proceeding with the regulator parts, wire-up the ref and bulk supplies and confirm that they are producing:
ref:  +12V, +5V, -12V relative to 0V/GND (black multimeter lead).
bulk: +12 or +24V (depending on switch position) relative to 0V (black multimeter lead).

[Therm Mr.]

@pqass there is a lot of good info there I will need to digest. I am going to need to study and think about it for a while before I reply. I thought had a better understanding of T1 from a few previous posts with Kleinstein. But I went back and re-read them I realized I had mis-understood what he said. I only absorbed 1/2 of the reply.

I do have few unrelated questions though.

Fuses F-1 and F-2 call for 1 amp 125v solder in fuses, which I found some Littlefuse for. But it list's F-3 as a fusible resistor 1 ohm 5% .5 watt. Is there a different name for this? Because I can not find fusible resistors anywhere?

And it lists the main T-1 fuse F-4 as a 1 amp or 2 amp in a fuse holder. Size depending on if its OE9 or OE3 and I don't understand what that means. The Transformer is 48 VA which I calculate as .4 amps at 120v so I assume the 1 amp is the correct fuse. Am I correct?

Thanks

Therm

[Kleinstein]

Fusible resistors may be a replacement for low current fuses. For a new build it should be OK to use a suitable low current slow fuse (what ever the transformer can support). The values will depend on the display part.
Fusible resistors are still available, though not longer that common. PTC type fuses can be an alternative in some cases, though the characteristinc and use  is different.

For F1 and F2 it is OK to used exchangible fuses with holder instead of a direct solderable. For DIY this may be easier to get.


The input side fuse depends on the line voltage setting: with 230 V main a smaller fuse is sufficient and should be used. 1 A sounds OK, as the transformer can have some turn on spike in the current, both from the transformer and charging the filter capacitors.